The purposes of the study are (1) Assess the effectiveness of chronic electrical stimulation of midbrain sites for the relief of chronic pain in humans; (2) Evaluate the efficacy and mechanisms of traditional narcotic analgesia and compare these to chronic electrical stimulation of midbrain sites; (3) Validate experimental models of pain and their potential diagnostic use in chronic pain patients; and (4) Determine and compare the impact of both traditional narcotic and chronic electrical stimulation therapies on the functional, intellectual and emotional well being of these patients. The effects of chronic brain stimulation in surgical patients will be compared to the effects of narcotics previously administered to patients and to effects of narcotic regimes in non-surgical chronic pain patients. In addition, the effects of narcotics on perceptual and neural mechanisms of experimentally induced pain will be assessed in pain-free volunteers. The results from two patients this year continue to support previous findings from this project. Morphine significantly decreased the magnitude of both low back pain and experimentally administered heat pain and this effect was reversed by naloxone. Comparison of these results to those found after deep brain stimulation suggest that deep-brain stimulation analgesia is not opioid mediated and is either less potent that morphine analgesia or follows a different course. A second study compared the influence of the narcotic fentanyl on reaction time measures to heat pain in normal subjects to results found previously with chronic pain patients. The results show that fentanyl decreases the magnitude of both first and second pain sensations in a manner similar to decreases found in chronic patients after administration of morphine.